Representative photomicrographs of (a) a fibroadenoma (FA) and (b) a benign phyllodes tumor (BePT) from this series. Scale bars, 100 μm (c) Frequency of MED12 exon 2 mutations in FAs (n=21) and BePTs (n=8) in adolescents and young adults, identified by Sanger sequencing. (d) MED12 protein domain structure and detailed view of exon 2, depicting the 13 and 7 mutations identified in the 21 FAs and 8 BePTs from this study, respectively. aa, aminoacid; BePTs, benign phyllodes tumors; SNV, single-nucleotide variant.